Methods of producing ultra -low resistivity tantalum films.

ABSTRACT

We have discovered that, by depositing a tantalum layer upon a substrate at a temperature of at least 325° C., it is possible to obtain an ultra low resistivity which is lower than that previously published in the literature. In addition, it is possible deposit a Ta x N y  film having an ultra low resistivity by depositing the Ta x N y  film upon a substrate at a temperature of at least 275° C., wherein x is 1 and y ranges from about 0.05 to about 0.18. These films having an ultra low resistivity are obtained at temperatures far below the previously published temperatures for obtaining higher resistivity films. A combination of elevated substrate temperature and ion bombardment of the film surface during deposition enables the use of lower substrate temperatures while maintaining optimum film properties. In another development, we have discovered that the ultra low resistivity tantalum and Ta x N y  films produced by the method of the present invention also exhibit particularly low residual stress, so that they are more stable and less likely to delaminate from adjacent layers in a multilayered semiconductor structure. Further, these films can be chemical mechanical polished at significantly higher rates (at least 40% higher rates) than the higher resistivity tantalum and Ta x N y  films previously known in the industry. This is particularly useful in damascene processes when copper is used as the interconnect metal, since it reduces the possibility of copper dishing during a polishing step.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention pertains to tantalum films having ultra-lowresistivity, in the range of about 10 μΩ-cm, as well as methods fordepositing ultra-low resistivity tantalum films. Tantalum filmsdeposited according to the method of the invention can be removed from asemiconductor substrate surface using chemical mechanical polishing(CMP) techniques far more rapidly than previously known tantalum films.

[0003] 2. Brief Description of the Background Art

[0004] As microelectronics continue to miniaturize, interconnectionperformance, reliability, and power consumption has become increasinglyimportant, and interest has grown in replacing aluminum alloys withlower resistivity and higher reliability metals. Copper offers asignificant improvement over aluminum as a contact and interconnectmaterial. For example, the resistivity of copper is about 1.67 μΩ-cm,which is only about half of the resistivity of aluminum.

[0005] One of the preferred technologies which enables the use of copperinterconnects is the damascene process. This process for producing amulti-level structure having feature sizes in the range of 0.5 micron(μm) or less typically includes the following steps: blanket depositionof a dielectric material over a substrate; patterning of the dielectricmaterial to form openings; deposition of a diffusion barrier layer and,optionally, a wetting layer to line the openings; deposition of a copperlayer onto the substrate in sufficient thickness to fill the openings;and removal of excessive conductive material from the substrate surfaceusing chemical-mechanical polishing (CMP) techniques. The damasceneprocess is described in detail by C. Steinbruchel in “Patterning ofcopper for multilevel metallization: reactive ion etching andchemical-mechanical polishing”, Applied Surface Science 91 (1995)139-146.

[0006] The preferred barrier layer/wetting layer for use with coppercomprises a tantalum nitride—tantalum barrier/wetting layer having adecreasing nitrogen content toward the upper surface of the layer. Thisstructure, which provides excellent barrier properties while increasingthe <111> content of an overlying copper layer, provides a copper layerhaving improved electromigration resistance, as described in applicants'copending application Ser. No. 08/995,108. A barrier layer having asurface which is essentially pure tantalum or tantalum including only asmall amount of nitrogen (typically less than about 15 atomic percent)performs well as a barrier layer and also as a wetting layer to enhancethe subsequent application of an overlying copper layer.

[0007] Philip Catania et al. in “Low resistivity body-centered cubictantalum thin films as diffusion barriers between copper and silicon”,J. Vac. Sci. Technol. A 10(5), September/October 1992, describes theresistivity of thin bcc-tantalum films and β-tantalum films. Theresistivity for bcc-tantalum (α-tantalum) films is said to be on theorder of 30 μΩ-cm, while the resistivity of the β-tantalum films rangesfrom about 160-180 μΩ-cm. A comparison of the effectiveness of thinbcc-Ta and β-Ta layers as diffusion barrier to copper penetration intosilicon shows that the bcc-Ta which exhibits low resistivity alsoperforms well as a barrier layer up to 650° C.

[0008] Kyung-Hoon Min et al. in “Comparative study of tantalum andtantalum nitrides (Ta₂N and TaN) as a diffusion barrier for Cumetallization”, J. Vac. Sci. Technol. B 14(5), September/October 1996,discuss tantalum and tantalum nitride films of about 50 nm thicknessdeposited by reactive sputtering onto a silicon substrate. Theperformance of these films as a diffusion barrier between copper andsilicon is also discussed. The diffusion barrier layer performance issaid to be enhanced as nitrogen concentration in the film is increased.

[0009] U.S. Pat. No. 3,607,384 to Frank D. Banks, issued Sep. 21, 1971,describes thin film resistors which utilize layers of tantalum ortantalum nitride. FIG. 1 in the '385 patent shows the resistivity for aparticular tantalum nitride film as a function of the sputtering voltageand FIG. 2 shows the resistivity as a function of the nitrogen contentof the film. The lowest resistivity obtained under any conditions wasabout 179 μΩ-cm.

[0010] U.S. Pat. No. 3,819,976 to Chilton et al., issued Jun. 25, 1974,describes a tantalum-aluminum alloy attenuator for traveling wave tubes.In the background art section of this patent, there is a reference totantalum film undergoing a phase transition from beta-tantalum tobody-centered-cubic (alpha) tantalum at about 700° C.

[0011] U.S. Pat. No. 3,878,079 to Alois Schauer, issued Apr. 15, 1975,describes and claims a method of producing thin tantalum films which arebody-centered cubic lattices. The films are deposited upon a glasssubstrate, and FIG. 2 of the '079 patent shows resistivity for tantalumnitride films as a function of nitrogen content. U.S. Pat. No. 4,000,055to Kumagai et al., issued Dec. 28, 1976, discloses a method ofdepositing nitrogen-doped beta-tantalum thin films. FIG. 2 of the '055patent also shows the resistivity of the film as a function of thenitrogen content of the film.

[0012] U.S. Pat. No. 4,364,099 to Koyama et al., issued Dec. 14, 1982,discloses a tantalum film capacitor having an α-tantalum as a lowerelectrode, a chemical conversion layer of α-tantalum as a dielectric,and an upper electrode. This references also discusses a phasetransition of the tantalum film depending on the nitrogen concentrationof the film. When the nitrogen content ranges from about 6 to about 12percent, the resistivity of the tantalum thin film is said to beadvantageously low, although no particular resistivity data is provided.

[0013] U.S. Pat. No. 5,221,449 to Colgan et al., issued Jun. 22, 1993,describes a method of making alpha-tantalum thin films. In particular, aseed layer of Ta(N) is grown upon a substrate by reactive sputtering oftantalum in a nitrogen-containing environment. A thin film of α-tantalumis then formed over the Ta(N) seed layer. In the Background Art sectionof the patent, reference is made to the “Handbook of Thin FilmTechnology”, McGraw-Hill, page 18-12 (1970), where it is reported thatif the substrate temperature exceeds 600° C., alpha phase tantalum filmis formed. Further reference is made to an article by G. Feinstein andR. D. Huttemann, “Factors Controlling the Structure of SputteredTantalum Films”, Thin Solid Films, Vol. 16, pages 129-145 (1973). Theauthors are said to divide substrates into three groups: Group I,containing substrates onto which only beta-tantalum can be formed(including glass, quartz, sapphire, and metals such as copper andnickel); Group II, containing substrates onto which only alpha (bcc)tantalum can be grown (including substrates coated with 5000 Å thickmetal films such as gold, platinum, or tungsten); and Group III,containing substrates which normally produce alpha-tantalum, but whichcan be induced to yield beta-tantalum or mixtures of alpha and beta bysuitable treatment of the surface (i e., substrates coated with 5,000 Åof molybdenum, silicon nitride, or stoichiometric tantalum nitride,Ta₂N).

[0014] As the feature size of semiconductor devices becomes eversmaller, the barrier/wetting layer becomes a larger portion of theinterconnect structure. In order to maximize the benefit of copper's lowresistivity, the diffusion barrier/adhesion layer must be made very thinand/or must have low resistivity itself (so that it does not impact theeffective line resistance of the resulting metal interconnectstructure). As is readily apparent, depending on the device to befabricated, various methods have been used in an attempt to develop atantalum film which is α phase when lower resistivity is desired.Typically, small additions of nitrogen have been made to tantalum filmsto lower the resistivity of the tantalum. This method is difficult tocontrol, as any deviation in the nitrogen content (even ±1 sccm ofnitrogen flow) may lead to a significant increase in resistivity.Another proposed sputter deposition method for lowering resistivityinvolves control of the ion energy striking the substrate (via groundingof the substrate). However, this method does not always producereproducible results, is sensitive to substrate cleaning andpreparation, and affects the film stress. Care must be taken to avoidhigh film stress so that the barrier/wetting layer does not tend toseparate or pop off the substrate upon which it is deposited.

[0015] After deposition of the tantalum-comprising barrier/wettinglayer, any of the tantalum-comprising material deposited on thesubstrate in areas other than the conductive interconnect structuresmust be removed. Whether the tantalum-comprising material is removed byion bombardment techniques (e.g., reactive ion etching) or by CMP, thedifference in hardness between the tantalum-comprising material andcopper causes problems. Residual material from the copper deposition israpidly removed, leaving residual material from the tantalum-comprisingbarrier layer. Continued ion bombardment or CMP to remove thetantalum-comprising material can result in the undesired removal ofadjacent copper which is intended to make up the interconnect structure.

[0016] It would be highly desirable to have an ultra-low resistivitytantalum film which exhibits low stress (tends to stay bonded tounderlying layers), and which is more easily polished using CMP, so thatits polishing rate is closer to that of copper.

SUMMARY OF THE INVENTION

[0017] We have discovered that, by depositing a tantalum layer atparticular substrate temperatures, it is possible to obtain a lowerresistivity than has previously been known in the literature. The lowresistivity material has been obtained by sputter deposition at anelevated substrate temperature ranging from about 325° C. to about 550°C., or by sputter deposition at a substrate temperature of less thanabout 325° C. followed by annealing at a temperature of about 325° C. orgreater. High density plasma sputtering techniques which provide for ionbombardment of the film surface can be used in combination with theelevated substrate temperature, to add momentum energy to the filmsurface, thereby reducing the substrate temperature required, whilestill providing the ultra-low resistivity tantalum film. A reduction ofabout 40% in the required substrate temperature can be obtained by thismeans, while maintaining a reasonable film stress and a reasonable filmdeposition time period.

[0018] In a less preferred, alternative method, a small amount (lessthan about 15 atomic %) of nitrogen may be added to the tantalum film(while depositing the film at an elevated temperature) to obtain thelower resistivity at a slightly lower substrate temperature, in therange of about 275° C. This provides a lower resistivity than previouslyknown for nitrogen addition, while reducing the process temperaturenecessary to obtain the lower resistivity.

[0019] In another development, we have discovered that the tantalumlayer produced by the method of the present invention can be morereadily removed by the CMP polishing techniques used for removal ofexcess, residual metal in the damascene process. The low resistivitytantalum is more flexible, more easily cleaved, and more easilypolished—an advantage in the damascene process when it is desired toremove excess metal from the field surface of a device structure. Thisis particularly helpful when copper is used as the interconnect metal,since copper polishes easily and it previously took 4 times longer toremove tantalum barrier layer then to remove excess copper from a fieldsurface. The low resistivity tantalum deposited using the present methodexhibits an increase in CMP polishing rate of nearly 50% over thepreviously known CMP polishing rate for tantalum films.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 shows a schematic cross-sectional view of a sputteringchamber of the kind which can be used to deposit the tantalum film ofthe present invention. This illustration shows the critical elements ofa high density plasma (ion-deposition) sputtering chamber (orreactive-ion-deposition sputtering chamber). The critical elementsinclude a sputtering target to with DC power is applied, an RF poweredcoil for creating and maintaining ionized species within a plasma overthe surface of the semiconductor substrate being processed, and a meansfor application of RF power to the support platen on which the substratesets, enabling the creation of a bias on the substrate. The combinationof the RF powered coil with the RF powered support platen enables theion bombardment of a film surface as the tantalum film is deposited.

[0021]FIG. 2 is a graph showing the resistivity of a sputter-depositedtantalum film (deposited using long-throw or high density plasmatechniques) as a function of the substrate platen heater temperatureduring deposition of the film. The substrate surface temperature isestimated to have been between 50° C. to 75° C. colder than thesubstrate platen heater temperature illustrated.

[0022]FIG. 3 is a graph showing the resistivity of a sputter-depositedtantalum film (deposited using long-throw or high density plasmatechniques), where the tantalum was deposited at room temperature, thenannealed for 15 minutes at 400° C. or 600° C.

[0023]FIG. 4 is a graph showing the resistivity of a sputter-depositedTa_(x)N_(y) film (deposited using long-throw or high density plasmatechniques) as a function of the substrate platen heater temperatureduring deposition of the film, wherein x is 1 and y ranges from about0.05 to about 0.18.

[0024]FIG. 5 is a graph showing the stress (in dynes/cm²) of asputter-deposited tantalum film (deposited using long-throw or highdensity plasma techniques) as a function of the substrate platen heatertemperature during deposition of the film.

[0025]FIG. 6 is a graph showing the chemical-mechanical polishing (CMP)removal rate (in Å/min) of a sputter-deposited tantalum film (depositedusing long throw or high density plasma techniques) as a function of thesubstrate platen heater temperature. FIG. 6 also shows the CMP polishingrate for two Ta_(x)N_(y) films which were deposited at a substrateplaten heater temperature of about 50° C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] We have discovered a surprising and simple method for depositingultra-low resistivity (about 10 μΩ-cm) tantalum films. These films canbe obtained by either sputter deposition upon a substrate which is at anelevated temperature or by a combination of deposition upon a substrateat such elevated temperature with simultaneous ion bombardment of thefilm surface during deposition.

[0027] Tantalum films having a slightly higher resistivity (about 20μΩ-cm) can be obtained by deposition at low temperature (e.g. roomtemperature), followed by thermal annealing. Deposition at an elevatedtemperature is preferred for process throughput reasons and because alower resistivity is obtained.

[0028] Deposition of a 1,000 Å thick tantalum film using high densityplasma or long-throw sputtering upon a silicon dioxide substrate, at asubstrate support platen temperature of about 400° C. or higher (asubstrate temperature of about 325° C. or higher) results in a tantalumfilm resistivity of about 10 μΩ-cm. (Deposition of thinner films underthe same conditions provides the same low resistivity.) This is comparedwith a film resistivity of about 165 μΩ-cm obtained for a tantalum filmsputtered upon a room temperature substrate. In addition, deposition ofthe tantalum film at room temperature, followed by a 15 minute anneal ata substrate temperature of either 350° C. or 550° C., produces atantalum film having a resistivity of about 20 μΩ-cm.

[0029] We have also discovered that by adding a small amount of nitrogento the sputtering chamber, to produce a Ta_(x)N_(y) film where x is 1and y ranges from about 0.5 to about 0.18, a Ta_(x)N_(y) film having aresistivity of about 20 μΩ-cm can be obtained at even lowertemperatures, particularly at a substrate temperature of about 275° C.or greater.

[0030] Although tantalum and tantalum nitride are quickly gainingindustry acceptance as the barrier layer of choice for coppermetallization, the difference in CMP polishing rate between copper andthese materials causes problems in the damascene process for preparationof copper interconnect structures. The softer copper, which polishesmore rapidly tends to “dish”, i.e. to be removed from an intendeddeposition area during the polishing period necessary for removal ofexcess barrier layer materials. We have discovered that the lowresistivity α phase tantalum produced by the method of the presentinvention (described above) shows a CMP rate superior to standard βphase tantalum and more similar to that of tantalum nitride. This makesit possible to use tantalum as the barrier layer and to use thickertantalum barrier layers.

[0031] A more detailed description of the ultra-low resistivity tantalumfilms and methods for their deposition is presented below.

[0032] I. Definitions

[0033] As a preface to the detailed description, it should be notedthat, as used in this specification and the appended claims, thesingular forms “a”, “an”, and “the” include plural referents, unless thecontext clearly dictates otherwise. Thus, for example, the term “asemiconductor” includes a variety of different materials which are knownto have the behavioral characteristics of a semiconductor.

[0034] Specific terminology of particular importance to the descriptionof the present invention is defined below.

[0035] The term “aspect ratio” refers to, but is not limited to, theratio of the height dimension to the width dimension of particularfeature. When the feature has more than one width dimension, the aspectratio is typically calculated using the smallest width dimension of thefeature. For example, a contact via opening which typically extends in atubular form through multiple layers has a height and a diameter, andthe aspect ratio would be the height of the tubular divided by thediameter. The aspect ratio of a trench would be the height of the trenchdivided by the minimal width of the trench, which typically occurs atits base.

[0036] The term “collimated sputtering” refers to, but is not limitedto, collimated sputtering where a spatial filter or ‘collimator’,comprising a plurality of transmissive cells, is positioned between thesputtering target and the substrate to prevent sputtered particles fromreaching the substrate surface at low angles of incidence. The spatialfilter controls the location at which sputtered emissions are depositedupon the substrate surface. This serves to create a more directionalflux to the substrate.

[0037] The term “copper” includes, but is not limited to alloys ofcopper of the kind typically used in the semiconductor industry. Thepreferred embodiments described herein are with reference to a copperalloy comprising about 98% by weight copper, but the invention can beused in combination with other conductive materials which exhibit asubstantially smaller copper content. For example, the invention can beused where the metallization layer comprises aluminum-copper alloys,where the copper content is typically less than about 4 weight %, andaluminum-copper-silicon alloys, where the copper content is typicallyabout 0.5 weight %.

[0038] The term “decoupled plasma source” refers to a plasma generationapparatus which has separate controls for power input to a plasma sourcegenerator and to a substrate bias device. Typically the plasma sourcecontroller controls the supply of inductively coupled RF power whichdetermines plasma density (source power) and the bias controllercontrols the supply of RF power or DC power which is used to generate aDC bias voltage on the semiconductor substrate surface (bias power). Thebias voltage affects the ion bombardment energy on the substratesurface. This decoupled plasma source typically incorporates measures toseparate (decouple) the influence of the source power and bias power onone another. The ENDURA® metal deposition system and CENTURA® metal etchsystem available from Applied Materials, Inc. of Santa Clara, Calif.which includes decoupled plasma source power and bias power control arereferred to as “DPS” systems. Similar equipment available from othermanufacturers may be referred to by different nomenclature.

[0039] The term “feature” refers to, but is not limited to, contacts,vias, trenches, and other structures which make up the topography of thesubstrate surface.

[0040] The term “high density plasma sputter deposition” or “ion plasmadeposition” or “IMP sputter deposition” refers to, but is not limitedto, sputter deposition, preferably magnetron sputter deposition (where amagnet array is placed behind the target), where a high density plasmais created using the application of inductively coupled RF power whichis typically applied to a coil which is positioned between thesputtering cathode and the substrate support electrode. This arrangementprovides an increased portion of the sputtered emission is in the formof ions at the time it reaches the substrate surface. In high densityplasma deposition, the electron density is typically at least 10¹¹e⁻/cm³. A preferred apparatus for high density plasma sputter depositionis the ENDURA® “IMP” metal deposition system.

[0041] The term “ion deposited copper” or “IMP deposited copper” refersto a copper deposition which was sputtered using a high density plasmasputter deposition process.

[0042] The term “ion deposited Ta or Ta_(x)N_(y)” or “IMP deposited Taor Ta_(x)N_(y)” refers to a Ta or Ta_(x)N_(y) deposition which wassputtered using a high density plasma sputter deposition process.

[0043] The term “long-throw sputter deposition” refer to a sputterdeposition technique which utilizes conventional, non-collimatedmagnetron sputtering at low pressures, where the distance between thetarget and the substrate is equal to or greater than the diameter of thesubstrate. Long-throw (gamma) sputter deposition enables control of thedegree of directionality in the deposition of film layers, resulting inimproved step coverage as compared with conventional magnetronsputtering.

[0044] The term “reactive ion deposition” or “reactive ion metal plasma”refers to ion-deposition sputtering wherein a reactive gas is suppliedduring the sputtering to react with the ionized material beingsputtered, producing an ion-deposition sputtered compound containing thereactive gas element.

[0045] The term “SEM” refers to a scanning electron microscope.

[0046] The term “standard copper deposition” or “traditional sputtering”refers to a method of forming a film layer on a substrate wherein atarget is sputtered and the material sputtered from the target passesbetween the target and the substrate to form a film layer on thesubstrate, and no means is provided to ionize a substantial portion ofthe target material sputtered from the target before it reaches thesubstrate. One apparatus configured to provide traditional sputtering isdisclosed in U.S. Pat. No. 5,320,728, the disclosure of which isincorporated herein by reference. In such a traditional sputteringconfiguration, the percentage of ionized target material which reachesthe substrate is less than 10%, more typically less than 1%, of thatsputtered from the target.

[0047] The term “tantalum film” refers to a film wherein at least 98atomic % of the film is tantalum.

[0048] The term “Ta_(x)N_(y)” refers to a material wherein x representsthe number of tantalum atoms and y represents the relative number ofnitrogen atoms.

[0049] II. An Apparatus for Practicing the Invention

[0050] A process system in which the method of the present invention maybe carried out is the Applied Materials, Inc. (Santa Clara, Calif.)Endura® Integrated Processing System. This process system is notspecifically shown in the Figures. However, the system is generallyknown in the semiconductor processing industry and is shown anddescribed in U.S. Pat. Nos. 5,186,718 and 5,236,868, the disclosures ofwhich are incorporated by reference. The critical elements of a reactiveion metal plasma sputter deposition system are shown in a schematicformat in FIG. 1. Process chamber 100 is used for the high densityplasma deposition of a barrier layer such as a Ta or a Ta_(x)N_(y)layer.

[0051] Process chamber 100 is typically a magnetron chamber whichemploys a standard sputter magnet (not shown) to confine the sputteringplasma, enabling an increased sputtering rate. In addition, the processchamber includes an inductively coupled RF source 110, typically in theform of a single, flat coil 108, positioned between a sputtering cathode(target) 102 and the substrate support electrode 104, whereby a largerportion of the sputtered emission is in the form of ions at the time itreaches the substrate surface. An RF power source 106 is used to apply abias to substrate support electrode 104, enabling formation of a DC biason semiconductor substrate 105. Typically a shield 113 surrounds thearea in which plasma 107 is created from gases which enter throughchannels 103. Shield 113 is surrounded by a vacuum chamber 112 whichenables the evacuation of gases from the substrate processing areathrough evacuation channels (not shown). In the preferred embodiment ofthe present invention where the barrier layer to be formed isTa_(x)N_(y), the tantalum nitride is formed by sputtering a tantalumtarget using techniques known in the art, where argon is gas used tocreate sputtering ions, and by adding nitrogen to the process chamber100 through channels 103. At least a portion of the nitrogen is ionizedas it passes by ionization coil 108. The reactive nitrogen is free toreact with reactive tantalum to form tantalum nitride which is thenattracted toward the surface of semiconductor substrate 105 by the biasplaced on that substrate.

[0052] III. The Ultra-Low Resistivity Tantalum Films

[0053] The tantalum films of the invention have a resistivity of lessthan 25 μΩ-cm; more preferably, less than 20 μΩ-cm; most preferably,less than 15 μΩ-cm. Resistivities as low as 10 μΩ-cm or less have beenachieved using the deposition methods of the invention.

[0054] Curve 200, FIG. 2, shows the resistivity (on vertical axis 202)of sputter-deposited tantalum films (deposited via collimated, orlong-throw, or high density plasma techniques) as a function of thesubstrate platen heater temperature (on vertical axis 204) duringdeposition of the film. (The substrate surface temperature is estimatedto have been about 50° C. to about 75° C. colder than the substrateplaten heater temperature illustrated.) The tantalum films representedby portion 206 of curve 200, where the tantalum resistivity is greaterthan 100 μΩ-cm, were determined to be β-tantalum. The tantalum filmsrepresented by portion 208 of curve 200, where the resistivity is lessthan 25 μΩ-cm, were determined to be α-tantalum (body-centered cubictantalum). The ultra low resistivity films were obtained when thesubstrate platen heater temperature was about 400° C. (representing asubstrate temperature of about 325° C.-350° C.) or higher.

[0055]FIG. 3, at point 306, shows the resistivity of a sputter-depositedtantalum film (deposited via collimated, or long-throw, or high densityplasma techniques) deposited at room temperature (about 25° C.). Onceagain, the resistivity is shown on vertical axis 302 and the substrateplaten heater temperature is shown on horizontal axis 304. This sputterdeposited tantalum film, when annealed on the substrate support platenfor a time period of about 15 minutes at a heater temperature of about400° C. or higher, exhibits a resistivity of less than about 20 μΩ-cm,as illustrated by curve 308.

[0056]FIG. 4 shows the resistivity of collimated, or long-throw, or highdensity plasma deposited films having a Ta_(x) N_(y) composition, wherex is 1 and y ranges from about 0.05 to about 0.18. The resistivity isshown as a function of the substrate platen heater temperature duringsputtering. Once again, the resistivity is shown on vertical axis 402and the substrate platen heater temperature is shown on horizontal axis404. The substrate temperature is typically about 50° C. to about 75° C.lower than the substrate platen heater temperature. With the nitrogenpresent in the sputtered film, it is possible to obtain the ultra lowresistivity Ta_(x) N_(y) film at even lower deposition temperatures.Ta_(x) N_(y) films having a resistivity of about 20 μΩ-cm were obtainedat substrate heater temperatures of about 340° C. or higher (substratetemperatures of about 275° C. or higher).

[0057] The ultra-low resistivity films of the present invention tend tobe low stress films as well. FIG. 5 is a graph showing the stress (indynes/cm² on vertical axis 502) of a sputter-deposited tantalum film asa function of the substrate platen heater temperature (in ° C. onhorizontal axis 504) during deposition of the film. As can be seen fromthe graph in FIG. 5, tantalum films deposited at heater temperatureswithin the range of about 365° C. to about 500° C. had low tensilestresses ranging from about −2.5×10⁹ to about 5×10⁹ dynes/cm². Thenegative stress values, represented by area 510 under line 507 representtantalum films in compression. The positive stress values, representedby area 508 over line 507 represent tantalum films in tension. Bymaintaining the heater temperature at about 365° C. or higher duringdeposition of the film, the stability of the deposited film and itsadhesion to adjacent substrates is improved.

[0058] Unexpectedly, we discovered that the tantalum films of thepresent invention can be polished more rapidly using CMP techniques andare more flexible when cleaved than the prior art tantalum films. FIG. 6shows the chemical-mechanical polishing (CMP) removal rate (in Å/min onvertical axis 602) of a sputter-deposited tantalum film (deposited viacollimated, or long-throw, or high density plasma techniques, with orwithout nitrogen) as a function of the substrate platen heatertemperature (in ° C. on horizontal axis 604). The CMP removal rate ofTa_(x)N_(y) (in Å/min on vertical axis 602) as a function of nitrogencontent (in atomic % of the film on horizontal axis 605), when depositedat a heater temperature of about 50° C. Tantalum films deposited at aheater temperature of 50° C. had a CMP removal rate of about 230 Å perminute; Ta films deposited at a heater temperature of 350° C. had a CMPremoval rate of about 280 Å per minute; and, Ta films deposited at aheater temperature of 500° C. had a CMP removal rate of about 340 Å perminute. Extrapolating from the graph in FIG. 6, tantalum films depositedat a heater temperature within the range of about 375° C. to about 500°C. (representing a substrate temperature within the range of about300-450° C.) would have a CMP removal rate in the range of about 300 toabout 340 Å per minute, which is significantly better than the CMPremoval rate of 230 Å per minute obtained for Ta films deposited at aheater temperature of 50° C.

[0059] Referring again to the graph in FIG. 6, tantalum films containingabout 18 atomic percent nitrogen had a CMP removal rate of about 250 Åper minute. Tantalum films containing about 37 atomic percent nitrogenhad a CMP removal rate of about 350 Å per minute. However, these filmsdo not offer the low resistivity of the Ta films of the presentinvention.

[0060] The ultra-low resistivity tantalum films of the invention areparticularly suited for use as barrier/adhesion layers for use in coppermetallization, in high stability conductive films for integrated circuitdevices (e.g., gate material to DRAMs, etc.), in thin film resistors,and in ink jet heads, by way of example and not by way of limitation.

[0061] IV. Methods for Depositing the Ultra-low Resistivity TantalumFilms

[0062] A preferred embodiment method of the invention comprises sputterdepositing a tantalum film on a substrate at a substrate temperature ofabout 325° C. or greater; preferably, at a substrate temperature withinthe range of about 350° C. to about 450° C.

[0063] In a second preferred embodiment method, in addition to sputterdepositing a tantalum film on a substrate at an elevated temperature,the surface of the film is ion bombarded during deposition to transfermomentum energy to the film surface. This permits deposition of the filmat a temperature which is about 40% lower than when ion bombardment isnot used.

[0064] In a first, less preferred alternative method, the tantalum filmis sputter deposited at room temperature (about 25° C.), and the film issubsequently annealed at a temperature ranging from about 325° C. toabout 550° C. for a time period of about 1 minute to about 15 minutes(longer periods will also work).

[0065] In a second, less preferred alternative method, a Ta_(x)N_(y)film is sputter deposited on a substrate at an elevated temperature,where x is 1 and y ranges from about 0.05 to about 0.18 (nitrogen ispresent in the sputtering chamber in an amount which produces aTa_(x)N_(y) film containing between about 5 and about 15 atomic percentnitrogen). The elevated substrate temperature is about 275° C. orgreater; preferably, at a substrate temperature within the range ofabout 300° C. to about 400° C. It is expected that ion bombardment ofthe Ta_(x)N_(y) film surface during sputter deposition would permitdeposition of the film at a temperature which is about 40% lower, asdescribed with respect to tantalum.

[0066] In a third, less preferred alternative method, a Ta_(x)N_(y) filmwas sputter deposited on the substrate at approximately room temperature(i.e., at a substrate temperature within the range of about 15° C. toabout 50° C.), and then annealed by heating the film (and substrate) toa temperature within the range of about 325° C. to about 550° C. for aperiod of about 1 minute to about 15 minutes (longer time periods willwork also).

[0067] The method of the present invention is not limited to aparticular sputtering technique. In addition to the sputteringtechniques described above, it is possible to use anexternally-generated plasma (typically generated by microwave) which issupplied to the film deposition chamber, or to use a hallow cathodetechnique of the kind known in the art. However, we have found that whenthe feature size is small (less than about 0.5 μm) and the aspect ratiois high (about 2:1 or higher), it is advantageous to use collimated,long-throw, or high density plasma sputter deposition in the apparatuswhich is described in detail herein.

[0068] Typical process parameters for high density plasma sputterdeposition, collimated sputter deposition, and long-throw sputterdeposition of the ultra-low resistivity tantalum films are set forth inTable 1, below. TABLE 1 Typical Process Conditions for SputterDeposition of Ultra-low Resistivity Tantalum Films in ENDURA ® ProcessChamber High Denisty Long-throw Process Parameter Plasma Collimated(Gamma) Process Chamber 10-40 3-5 1-3 Pressure (mT) DC Power to Target(kW) 1 4 4 RF Power to Coil (kW) 1.5 None None Bias Power (W) 350 NoneNone

[0069] An example of a high density plasma sputtering method is providedby S. M. Rossnagel and J. Hopwood in their papers “Metal ion depositionfrom ionized magnetron sputtering discharge”, J. Vac. Sci. Technol. B,Vol. 12, No. 1 (January/February 1994) and “Thin, high atomic weightrefractory film deposition for diffusion barrier, adhesion layer, andseed layer applications”, J. Vac. Sci. Technol. B, Vol. 14, No. 3(May/June 1996)

[0070] The technique for long throw sputtering is described by S. M.Rossnagel and J. Hopwood in their paper entitled “Thin, high atomicweight refractory film deposition for diffusion barrier, adhesion layer,and seed layer applications”, J. Vac. Sci. Technol., B 14(3), May/June1996. The method uses conventional, non-collimated magnetron sputteringat low pressures, with improved directionality of the depositing atoms.The improved directionality is achieved by increasing the distancebetween the workpiece surface (the throw), such that the distancebetween the target and the substrate is equal to or greater than thediameter of the substrate, and by reducing the argon pressure duringsputtering. For a film deposited with commercial cathodes (AppliedMaterials Endura® class; circular planar cathode with a diameter of 30cm) and rotating magnet defined erosion paths, a throw distance of 25 cmis said to be approximately equal to an interposed collimator of aspectratio near 1.0, to enable the aluminum to reach the bottom and sidewallsof the contact via structure without causing a bridge-over effect of thestructure experienced in some sputter deposition configurations. In thepresent disclosure, use of this long-throw technique with traditional,non-collimated magnetron sputtering at low pressures is sometimesreferred to as “gamma sputtering”.

[0071] A description of collimated sputtering is provided in U.S. Pat.No. 5,330,628 of Demaray et al., issued Jul. 19, 1994, and a method ofcontrolling a collimated sputtering source is described in U.S. Pat. No.5,478,455 to Actor et al. issued Dec. 26, 1995.

[0072] The method of the present invention is easily practiced in viewof the present disclosure, and does not require alteration of existingphysical vapor deposition (PVD) equipment presently available within theindustry. However, when it is desired to lower the substrate temperaturebelow about 325° C. during deposition of the tantalum film, it isnecessary to use high density plasma sputtering techniques which providefor ion bombardment of the film surface, to add momentum energy to thedepositing film surface. This enables lowering of the substrate surfacetemperature by as much as about 40%, while providing a reasonable filmdeposition time period.

[0073] The method of the invention results in the production of tantalumfilms and Ta_(x)N_(y) films having ultra-low bulk resistivities andminimal residual film stress. The method of the invention also providestantalum films which can be more rapidly polished using CMP techniques.The CMP rate of the tantalum films of the present invention is morecompatible with the CMP rate of copper, resulting in a reduction ofcopper dishing.

[0074] The above described preferred embodiments are not intended tolimit the scope of the present invention, as one skilled in the art can,in view of the present disclosure expand such embodiments to correspondwith the subject matter of the invention as claimed below.

We claim:
 1. A tantalum film having a resistivity of less than 25 μΩ-cm.2. A tantalum film according to claim 1, wherein said film has aresidual stress ranging between about 5.0×10⁹ and −5.0×10⁹ dynes/cm². 3.A tantalum film according to claim 1, having a chemical-mechanicalpolishing rate which is at least 40% increased over the polishing rateof a tantalum film having a resistivity of at least 100 μΩ-cm.
 4. Amethod of producing the tantalum film according to claim 1, or claim 2,or claim 3, wherein said film is produced by sputter deposition upon asubstrate at a temperature of about 325° C. or greater.
 5. The methodaccording to claim 4, wherein said sputter deposition is high densityplasma sputter deposition, and the surface of said tantalum film is ionbombarded during deposition, whereby said substrate temperature isreduced by as much as about 40% during said deposition without anincrease in the resistivity of said deposited tantalum film.
 6. Themethod according to claim 4, wherein said tantalum film is produced bysputter deposition upon a substrate at a temperature within the range ofabout 350° C. to about 550° C.
 7. The method according to claim 6,wherein said sputter deposition is high density plasma sputterdeposition, and the surface of said tantalum film is ion bombardedduring deposition, whereby said substrate temperature is reduced by asmuch as about 40% during said deposition without an increase in theresistivity of said deposited tantalum film.
 8. A method of producingthe tantalum film according to claim 1, wherein said film is produced bysputter deposition upon a substrate at a temperature of less than about325° C. and wherein said film is subsequently annealed at a temperaturegreater than about 325° C.
 9. A Ta_(x)N_(y) film having a resistivity ofless than 25 μΩ-cm, wherein x is 1 and y ranges from about 0.05 to about0.18.
 10. A Ta_(x)N_(y) film according to claim 9, wherein said film hasa residual stress ranging between about 5.0×10⁹ and −5.0×10⁹ dynes/cm².11. A Ta_(x)N_(y) film according to claim 9, having achemical-mechanical polishing rate which is at least 40% increased overthe polishing rate of a Ta_(x)N_(y) film having a resistivity of atleast 100 μΩ-cm.
 12. A method of producing the Ta_(x)N_(y) film of claim9, wherein said film is produced by sputter deposition upon a substrateat a temperature of about 275° C. or greater.
 13. A method of producingthe Ta_(x)N_(y) film according to claim 9, wherein said film is producedby sputter deposition upon a substrate at a temperature of less thanabout 275° C. and wherein said film is subsequently annealed at atemperature of about 275° C. or greater.
 14. A tantalum film accordingto claim 1, wherein said film has a chemical-mechanical polishing rateof at least 270 Å per minute.
 15. A Ta_(x)N_(y) film according to claim9, wherein said film has a chemical-mechanical polishing rate of atleast 270 Å per minute.
 16. A method of producing a sputtered tantalumfilm having a resistivity of less than 25 μΩ-cm, said method comprising:placing a substrate on a temperature-controlled support platen in aphysical vapor deposition process chamber; and controlling thetemperature of said support platen during the sputtering of saidtantalum film upon said substrate, in a manner such that said substratetemperature is about 325° C. or higher during deposition of saidsputtered tantalum film.
 17. The method according to claim 16, whereinsaid support platen temperature is controlled to be at an individualtemperature between about 350° C. and about 550° C. or is controlledover a temperature ranging between about 350° C. and about 550° C.
 18. Amethod of producing a sputtered Ta_(x)N_(y) film, said methodcomprising: placing a substrate on a temperature-controlled supportplaten in a physical vapor deposition process chamber; and controllingthe temperature of said support platen during the sputtering of saidTa_(x)N_(y) film upon said substrate, in a manner such that saidsubstrate temperature is about 275° C. or greater during deposition ofsaid sputtered Ta_(x)N_(y) film.
 19. The method according to claim 18,wherein said support platen temperature is controlled to be at anindividual temperature between about 275° C. and about 550° C. or iscontrolled over a temperature ranging between about 275° C. and about550° C.
 20. The method according to claim 16, wherein said sputterdeposition is high density plasma sputter deposition, and the surface ofsaid tantalum film is ion bombarded during deposition, whereby saidsubstrate temperature is reduced by as much as about 40% during saiddeposition without an increase in the resistivity of said depositedtantalum film.
 21. The method according to claim 18, wherein saidsputter deposition is high density plasma sputter deposition, and thesurface of said Ta_(x)N_(y) film is ion bombarded during deposition,whereby said substrate temperature is reduced by as much as about 40%during said deposition without an increase in the resistivity of saiddeposited Ta_(x)N_(y) film.